<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin:0;
            padding:0;
        }
        div{
            height:100px;
            /* 如果在范围内，正常取值 width */
            width:1000px;
            background-color: blue;
            /* 小于最小宽度，取最小宽度 */
            min-width:800px;
            /* 大于大宽度，取最大宽度 */
            max-width:1200px;

            border:1px solid red;
            border-width:10px;
        }
    </style>
</head>
<body>
    <div>111</div>
</body>
</html>